The present invention relates to a capacitive semiconductor sensor, such as an acceleration sensor (accelerometer) or a yaw-rate sensor, adapted to detect dynamic volume as a capacitance change.
As one of such conventional semiconductor capacitive sensors, a well-known accelerometer has such a stack structure that a plurality of semiconductor chips are laminated (stacked) (see FIGS. 10 and 11), which has already been disclosed as Japanese Patent Publication No. 2000-227439.
In this conventional capacitive semiconductor sensor, a sensor chip 1 having an acceleration detecting portion, as shown in FIGS. 12 and 13, is mounted on a circuit chip 2 with a signal processing circuit to be bonded. The circuit chip 2 is also bonded on the inner bottom surface of a package 3 having a concave shape in its vertical cross section so that the sensor chip 1 and the circuit chip 2 are contained in the package 3.
A number of electrode pads 1a, such as four, are formed on one peripheral end portion of the top surface of the semiconductor chip 1. A number of electrode pads 2a, such as four, are formed on one peripheral end portion of the top surface of the circuit chip 2. The positions of the electrode pads 1a correspond to those of the electrode pads 2a. 
The electrode pads 1a and the electrode pads 2a are electrically connected by bonding wires 4, respectively. Lead electrodes formed on, for example, both end portions of the top surface of the package 3 are electrically connected to corresponding lead electrodes formed on both end portions of the top surface of the circuit chip 2 by bonding wires 5, respectively.
In this configuration of the capacitive semiconductor sensor, the intervals between the adjacent bonding wires 4 are comparatively narrow, so that parasitic capacitances generating between the adjacent bonding wires 4 may comparatively increase.
In addition, because the bonding wire 4 is easily deformable, external impact may cause the bonding wires 4 to be deformed so that the parasitic capacitances may fluctuate. The fluctuation of the parasitic capacitances may affect the characteristic of the sensor 1, that is, the detection accuracy thereof. In order to prevent this affection, the electrode pads 1a may be formed on each peripheral end portion of the sensor chip's top surface to widen the intervals between the adjacent bonding wires 4. This configuration, however, may need to secure bonding areas on the top surface of the circuit chip 2, which causes the circuit chip's area to be enlarged, and the whole size of the circuit chip 2 to be enlarged.
Packaging of the conventional sensor must be designed while taking into consideration of bonding conditions including the loci of tools for bonding the bonding wires 4 and 5 so that the shape and size of the chips 1 and 2, and the package 3 are limited, respectively, which may cause the sensor's design freedom to decrease.
In the sensor with the above stack structure, as the sensor chip 1, a sensor chip that is as thin as possible is applied to prevent the whole thickness of sensor from being enlarged. This sensor chip, however, may have low rigidity so that it is apt to be distorted. The distortion of the sensor chip may have an effect on the acceleration detecting portion therein, causing errors in the values detected by the acceleration detecting portion.